This invention relates to appliances controlled by logic circuits such as microprocessor based control circuits. More specifically, this invention relates to such appliances featuring a self-diagnostic testing capability.
The use of microprocessor based controls in home appliances, such as clothes washers and dryers, dishwashers, and microwave ovens, is on the increase. In addition to providing greater number of user options in the normal operating mode, such controls also provide the capability for implementing a self-diagnostic test mode which can be useful as a testing tool in production to insure proper operation and facilitate factory adjustments and as an aid to household repair personnel in servicing such appliances in the field.
One example of a self-diagnostic feature may be found in commonly assigned U.S. Pat. No. 4,245,309 which discloses a microprocessor based control circuit for a washing appliance such as a dishwasher which includes a diagnostic system with a diagnostic routine which will sequence through the usual operating cycles in response to operator inputs and which may be advanced through the cycles at the operator's discretion. The cycle in progress and the malfunction, if any, is displayed on the control panel as the diagnostic routine is executed, facilitating diagnosis and repair. The service person initiates the self-diagnostic routine in this example through actuation of hidden switches on the control panel. U.S. Pat. No. 4,158,432 to van Bavel disclosed a self-diagnostic test feature for a microwave oven. This self-test feature causes the system to sequence through test routines whereby all the display lights are lit in a set order, then the displayed digits are actuated sequentially, keyboard inputs entered are displayed as a code, and the magnetron and broiler are turned on. This test routine is initiated by control switches built into the appliance but separate from the keyboard so that the keyboard can be bypassed, allowing testing of the keyboard itself. A further example of a self-diagnostic appliance control is disclosed in U.S. Pat. No. 4,275,464 to Schmidt. The control arrangement in Schmidt enables the microprocessor to perform self-diagnostic testing to locate trouble either in the internal circuitry or the external equipment and input and output devices connected to the microprocessor. To perform the self-diagnostic testing it is necessary for certain of the input and output leads from a microprocessor to some of the external circuits to be altered by removal of the external circuits to which they are associated and cross connection of the leads so that the self-diagnostic testing sequence can proceed. This is facilitated through use of a dummy plug containing cross connecting leads, resistors and capacitors, which plug could be a testing tool carried by an appliance service repair person, but is preferably provided as part of the appliance though not normally connected.
Self-diagnostic routines such as these can be provided primarily through appropriate programming of the microprocessor read only memory in microprocessor based controls. Since this aspect of the self-diagnostic feature requires no increase in hardware it has little impact on the cost of the control. However, means must be provided for enabling the factory worker or service person to initiate the diagnostic routine. As indicated by the foregoing examples, typically such means take the form of hidden switches or plugs or special connectors. The additional hardware and manufacturing costs associated with such routine initiating devices can have significant impact on control cost.
It would therefore be highly desirable to provide a control circuit arrangement which retains the advantages of the self-diagnostic test feature while eliminating the hardware cost associated with hidden switches or other devices incorporated in the appliance to enable the initiation of the self-diagnostic test routine.
It is, therefore, an object of this invention to provide an appliance control circuit having a self-diagnostic feature which is initiated by a simple inexpensive piece of test equipment external to the appliance which requires no special hardware modifications to the appliance itself to enable initiation. The simple test device would be universally applicable to all properly programmed appliance control circuits. Hence, a single testing device could be used by a service person to test numerous types of appliances provided only that the appliance control circuit be properly programmed.